A large number of curing agents are known for epoxy resins, as, for example, amines, anhydrides, mercaptans, etc. Each curing agent has advantages and disadvantages that make it acceptable or unusable for some applications. Also, each curing agent, or combination thereof, may be employed with one or more curing accelerators. Examples include the inorganic and organic metal salts such as lithium chloride and stannous octoate; onium salts such as ammonium chloride, alkyl phosphonium halides, etc; and BF.sub.3 complexes.
There is a need to develop curable epoxy resin compositions which cure very rapidly at moderably elevated temperatures yet have very long pot life at room temperature.
Accordingly, it has now been disclosed that certain trialkylsulfonium salts containing anions of low nucleophilicity function as excellent accelerators for the amine cure of epoxy resins. These accelerators are much more thermally latent than prior art accelerators such as BF.sub.3 complexes and give a much longer room temperature pot life at equivalent 150.degree. C. gel time. These systems have further been modified with additional monomers to give lower viscosity products.